1. Field of the Invention
This invention relates to a process of manufacturing a friction ring, which is intended for use in clutches or brakes and comprises a conical or cylindrical backing ring, which constitutes a hollow solid of revolution having inside and outside peripheral surfaces, and on at least one of said peripheral surfaces is provided with a sinter-bonded friction facing. In that process a blank for making the backing ring is blanked from flat sheet metal and is provided with a sinter-bonded friction facing, the backing ring provided with the sinter-bonded facing is deeply drawn to form a conical or cylindrical friction ring and the friction facing is embossed at the same time and is transformed with grooves distributed around the periphery of said facing.
2. Description of the Prior Art
It is known from U.S. Pat. No. 4,770,283 that friction rings which are intended for use in clutches or brakes and have a cylindrical or conical friction surface may comprise a friction facing which is directly sinter-bonded to a backing ring and that such friction rings can be made in that a blank for forming the backing ring is blanked from flat sheet metal and is provided with the sinter-bonded friction facing on at least one of its broadsides which are intended to constitute the conical or cylindrical peripheral surfaces of the backing ring, and only thereafter is the blank shaped between the die and a punch of a shaping tool set so that a friction ring having the desired conical or cylindrical shape is obtained. To ensure that the sinter-bonded friction facing will not adversely be affected by that shaping operation, angularly spaced apart embossing ribs are provided on the peripheral shaping surface of the punch and/or die of the shaping tool set so that the friction facing will be compacted and formed with grooves adjacent to said ribs hut the friction facing will not be compacted in the spaces between adjacent embossing ribs. As a result the sinter-bonded friction facing will not undesirably be compacted as the backing ring is deformed. In spite of said measure such friction rings have not proved satisfactory in practice because the required dimensional accuracy, particularly as regards the circularity and the true running of the ring, cannot consistently be ensured under the conditions of mass production. In that connection it must be borne in mind that the backing ring is usually made from a sheet steel blank, which is subjected to a heat treatment as the friction facing is sinter-bonded to the blank, and said heat treatment will necessarily result in a loss of strength of the blank so that the dimensional accuracy which can be achieved during the succeeding shaping step will adversely be affected.